I'm not sure either guy are totally wrong.
Doug Baldwin is one of the best pure slot WRs of the last decade and he echoes Troy Aikman's sentiments:
“The slot receiver’s kind of the quarterback of the receivers,” he said in 2015. “More so because the slot receiver has more responsibilities in terms of reading coverages and different adjustments based on what coverages you’re seeing. It’s a lot more complicated. … You have to know a lot more. You have to stay within the confines and the framework of the offense — you have a lot of freedom because you have a little bit more space, but at the same time, your job is usually to get someone else open, or to get open on a crucial down where it’s one-on-one. You have to be versatile, and you have to understand how your route goes into the concept, based on the different coverages you can see.”
All that said offenses have evolved even in the past 2-3 years. Now teams are moving their best players to the slot as a way to get them free releases or matched up with smaller (possibly lesser) CBs.
2018 data is known and used below....
For instance Michael Thomas who leads the NFL in productivity (and mean tweets) at the positions runs over half of his snaps from the slot.
So do Tyreek Hill, Larry Fitzgerald, Jarvis Landry, Keenan Allen, Julian Edelman, basically everyone for the Rams and well lots of guys you'd consider a WR1.
So now the slot is being used by the Chiefs, Rams, Cards and Pats to feature guys. Those are teams with innovative offensive coordinators and/or head coaches.
The slot is no longer about just holding your ground or playing a role to get open on 3rd down like Beasley did here in our dated offense.
It is about getting guys deep like Tyreek Hill.
Getting guys free releases for big plays at all levels like Michael Thomas.
It is about putting your best players in a position to succeed.
So what about Dallas..................
2018 Amari Cooper ran 30% of his routes from the slot, Michaal Gallup 15%.
Why? Dallas had a designated slot guy in Cole Beasley and they replaced him with a designated slot guy in Randall Cobb.
Beasley ran 90% of his routes out of the slot and Cobb and insane 93% in GB in 2018.
But modern offenses are changing that.
I expect MM too.
I think you'll see DAL use Cooper in the slot ~50% of the time. CeeDee also around 50%. --there will be over 100% to go around because formations will allow multiple slots on some plays.
Gallup likely stays outside as the designated WR2.
By going from Randall Cobb to Lamb to move form a guy who has trained solely as a slot to a guy who ran all 4 WR positions of the Air Raid, H(inside big/TE), Y(focal WR inside), X(lead outside WR), Z(Tall, outside big play guy)
This is exactly why I loved the CeeDee Lamb selection and would have HATED any other WR in round 1. Lamb has the ability day to play in a modern offense because they are air raid concepts that lend to slot domination.
This is also why many Air Raid teams had weak armed game readers.... No need to laser it when you are reading insider receivers being wide open 10-12 yards off the ball and inside the hashes.
BUT you take a Pat Mahomes and put him in that system and things.. CHANGE. Now your slinging it 50 air yards for fun. You are forcing teams to defend deep and play scared.
Baker Mayfield did this quite well. He is an assassin deep and very short but struggles in the old school median range. Baker killed teams with deep passes then underneath slots and crosses and WR screens of every sort.
Pat doesn't really struggle anywhere but in college had to score 50+ a week and had no OL. Tech needed him to be magic every drive so he made some mistakes on the way to the highest scoring offense virtually every year.
Dak also doesn't really struggle anywhere. He is definitely not Pat in his ease of flipping it out without form 35 yards, but he has great accuracy and arm strength on anything he gets his hips into. This is actually very much like Aikman.
Footwork was and is key for both as passers where accuracy and raw power merge.
So what might Dallas look like in 2020?
I think you'll see a varied passing attack that lines up Cooper and Lamb All Over the formation. X, Y, Z.
They can gameplan this weekly to attack defenses specific personnel and keep the looks changing on tape.
I can't remember being this excited about a Cowboys offense since the triplets ran their 5 plays taking what they wanted on the way to Super Bowls.